1. Field of the Invention
The present invention relates to a phosphor-containing molded member, a method of manufacturing the same, and a light emitting device having the phosphor-containing molded member.
2. Description of the Related Art
As a light emitting device using a fluorescent material or phosphor, there has been known a white light emitting device based on a combination of an LED chip emitting blue light and a YAG (yttrium aluminum oxide garnet) phosphor converting blue light to yellow light. The YAG phosphor is dispersed in an epoxy resin or silicone resin so as to be disposed around the LED chip. However, deterioration in the epoxy resin or silicone resin tends to occur with higher output power of an LED chip or generated heat from an LED chip. For this reason, there has been known a light emitting device using a glass having excellent thermal resistance and light resistance instead of epoxy resin or silicone resin, as described, for example, in JP2000-349340A, JP2000-349347A, JP2001-85747A, JP2004-200531, JP2003-258308A, and JP2006-202726A.
There has been known a conventional semiconductor light emitting device having a base substrate, a semiconductor light emitting element firmly fixed to the base substrate, and a coating material covering the semiconductor light emitting element, in which the coating material is polymetalloxane or ceramic having light transmissive property, as described, for example, in JP2000-349340A, JP2000-349347A, and JP2001-85747A. The coating materials described therein are glass mainly made of polymetalloxane bonding and contains a fluorescent material or phosphor. A coating material precursor solution is usually a liquid and forms a transparent coating material mainly made of a metalloxane bond of a metal oxide, due to decomposition of the components or absorbing of oxygen when heated in air or in an oxygen atmosphere. When a phosphor powder is mixed in such a coating precursor solution and the solution is applied around a semiconductor light emitting element, a coating material containing a phosphor which performs light conversion can be formed. The coating material precursor solution is typically injected in a recess of the base substrate and is calcined at a temperature in a range about 150° C. to 200° C. to solidify to form a coating material containing the phosphor so as to seal the semiconductor light emitting element. The calcination temperature of the coating material is sufficiently lower than the melting point of the semiconductor light emitting element. As described above, glass mainly formed with polymetalloxane bond has a low melting temperature so that the glass is in a liquid state at the time of sealing the semiconductor light emitting element. When the liquid glass solidifies, disconnection of the wire or detachment of the semiconductor light emitting element from the base substrate may occur due to the difference in expansion coefficient between each member.
There also has been known a conventional light emitting device in which an LED chip is mounted in a recess of a case made of ceramics, and a phosphor is applied around the LED chip by using a low melting point glass as a binder, as described, for example, in JP2004-200531A. The low melting point glass is applied around the LED chip and is melt by heat, then solidified. When the low melting point glass solidifies, disconnection of the wire or detachment of the LED chip from the case may occur due to the difference in expansion coefficient between each member. Moreover, the low-melting point glass has a poor light extraction efficiency. This is because the low-melting point glass has a color and a portion of the emitted light from the LED chip is absorbed by the colored portion of the low-melting point glass. Further, the low-melting point glass is susceptible to heat and humidity and has poor chemical stability.
There also has been known a conventional light emitting device having a blue light source and a emission color converting member, in which a part of blue light emitted from the blue light source is converted in yellow light which is combined with rest of the blue light to obtain white light, as described, for example, in JP2003-258308A. The emission color converting member is a glass having a softening point higher than 500° C., in which a Y3Al5O12 based inorganic phosphor is dispersed. To obtain the emission color converting member, first, an inorganic phosphor powder and glass powder are mixed to obtain an emission color converting member material. A resin binder is added to the emission color converting member material and pressure forming is performed to form a disk-shaped preform. The preform is fired to remove the resin binder and to sinter the preform into the emission color converting member. The sintering temperature of this perform is in a range of 400° C. to 850° C. In an example, the density of an inorganic phosphor contained in the glass is in a range of 0.05% by volume to 10.0% by volume. This emission color converting member is made by sintering an inorganic phosphor powder and a glass powder while removing a resin binder. Therefore, the inorganic phosphor cannot be contained at a high concentration. Because, if the inorganic phosphor is contained at a high concentration, the emission color converting member becomes very brittle.
Further, there has been known a conventional light emitting device having an ultraviolet LED element and an emission color converting member, in which ultraviolet light emitted from the ultraviolet LED element is converted into visible light, as described in JP2006-202726A. The emission color converting member is made by preparing an oxide glass power and a phosphor power in a compounding ratio of 90 to 10 by weight, or 95 to 5 by weight, to which a small amount of resin binder is added and mixed, then, the mixture is press-molded in a metal mold to form a button-shaped perform. The preform is sintered at a temperature in a range of plus or minus 150° C. of the softening point of the oxide glass to obtain a disk-shaped emission color converting member. Fluidity of glass at a temperature lower than the softening point of the oxide glass minus 150° C. is low, so that a dense sintered compact is difficult to obtain. At a temperature higher than the softening point thereof plus 150° C., the phosphor melts into the glass which may resulting in such as a low emission and discoloration of the glass. In a case where the compounding ratio of the phosphor powder with respect to the oxide glass powder is high, the obtained sintered compact will be very brittle.
Thus, the emission color converting members employing phosphor powder and glass powder used in the conventional light emitting devices have problems as described above.